Damper control for unit ventilator



July 15, 1958A F. G. BAKERA DAMPER CONTROL `FOR UNIT VENTILATOR FiledApril so, 1954 INVENTOR.

ATTY

United States Patent O DAMPER CONTROL FOR UNIT VENTILATOR Forrest G.Baker, Davenport, Iowa, assiguor to American Air Filter Company, Inc.,Louisville, Ky., a corporation of Delaware Application April so, 1954,serial No. 426,770

z claims. (c1. 236-49) This invention relates to self-contained roomventilating units. The invention has particular reference to a controlsystem for a room Ventilating unit of the type designed to maintain theroom temperature within a narrow -predetermined range by supplyingheated and unheated air to the room respectively when the roomtemperature falls below and rises above said range or a particular valuewithin that range.

Units of the type to which this invention relates comprises: a dampermovable between a damper closed or room-heating position-i. e. oneextreme position in which it closes an` inlet opening for unheated airand fully exposes or uncovers a heater to permit circulation of room airthrough it-to a damper open or roomcooling position-its other extremeposition in which it closes oit the room heater and fully exposes oruncovers the unheated air opening-control means normally set for apredetermined room temperature condition and normally operative inresponse to room temperature conditions rising above and falling belowsaid predetermined temperature conditions to move the damper in theopening and closing directions respectively, the control means includingan electrical control circuit and being normally operative when saidcircuit is energized, and a main switch unit for energizing anddeenergizing the control circuit. During normal room occupancy periods,these controls are quite satisfactory. During `those intervals in whichthe use of the unit is not desired, it may be shut down either manuallyby a manually operable main switch unit or automatically by a mainswitch unit in the form of the so called day-night control. When shutdown it will leave the damper in whatever position the damper may occupyat `that time and this is undesirable since the damper should be closedduring the shut down period.

The principal object of this invention is to provide a Ventilating unitof this general character in which the damper will move automatically toits closed position when the unit is shut down either manually orautomatically.

Another object is to provide an extremely simple and inexpensive meansfor electing the closure of the damper upon shutting down the unit.

The invention is illustrated in the accompanying drawings wherein:` Y

Figure l more or less schematically illustrates a conventionalVentilating unit to which this invention may be applied; and

Figure 2 illustrates a control system for the unit of Figure 1, thissystem embodying the present invention.

The structure illustrated in Figure 1 conventionally comprises: anoutside building wall 1 having an air inlet opening 2; and a Ventilatingunit 3 having a blower 4 for drawing air from its inlet chamber 5through an air lter 6 and the blower intake 7 so as to discharge thatair at 8 into the room. The blower 4 is operated by a motor 4a (Figure2). The inlet chamber 5 of the Unit contains .aA damper 10 mounted formovement from y 2,843,324 ICC Patented Jury-15, 195s one extreme damperclosed position-i. e. the full line position illustrated in Figure l-toa damper open position--i. e. the dotted line position illustrated inFigure 1.

. With the damper closed, the blower 4 operates to draw room air intothe inlet chamber 5 through heater 9 so that heated air is supplied tothe room. With the damper open, the blower 4 operates to `draw onlyunheated outside air through the opening 2. When the damper is in anintermediate position, it will draw both heated and unheated air inquantities depending upon the position it occupies.

The control for the Figure 1 structure is shown in Figure 2. lt broadlycomprises: a control means normally set for a predetermined temperaturecondition and normally operative, in response to temperature conditionsrespectively rising above and falling below said predeterminedtemperature conditions, to move said damper in the opening and closingdirections, said control means including an electrical control circuitand being normally operative when said circuit is energized; and a mainswitch unit for energizing and deenergizing said control circuit. Morespecically it includes: a damper operating motor; an electricmotor-operating circuit system for operating the motor in accordancewith the position of a motor control switch means, which is movable froma neutral position to damper closing and opening positions on oppositesides of neutral; balance means normally operative at a predeterminedtemperature condition to hold said switch means in neutral, said balancemeans i11- cluding yieldable means urging said switch means to its`damper closing position and a normally energized thermostaticallyresponsive electric control circuit system yieldably urging said switchmeans in opposition to said yield-v able means, said energized controlcircuit system being responsive to temperature conditions rising above`said predetermined temperature condition to move said switch meanstoward its damper opening position; and a power connection for both ofthe operating and control systems, including a main switch unit forenergizing and deenergizing said control system.

DAMPER MOTOR The damper operating motor is indicated at 15 and, asindicated, has a shaft 16 operatively connected to theA damper 10through a linkage including an arm or crank 17.

DAMPER MOTOR CIRCUIT SYSTEM open position, in4 accordance with a demandfor cool airto lower the room temperature; and contact 25 of the` motorcontrol switch. The counterclockwise damper closing circuit includes,`from lead line 20: motor winding 22` for counterclockwise rotation; alimit switch 24, which opens when the damper 10 has moved to its fullyclosed position iu accordance with a demand for hot air to raise theroom temperature; and contact 26 of the motor sition of the switch; andcontact arm 28 pivoted forr movement from the neutral position either to`adamper opening position on one side of neutral in which it 'en- Theclockwise damper open-` 3 gages `contact 25 of the damper openingcircuit to complete that circuit to lead line30, or, tov a damperclosing position on the other side of neutral in which it engagescontact 26 of the damper closing circuit to complete that circuit tolead 1ine.30.

BALANCE MEANS The balance means includes a yieldable means urging theswitch means toward the room heating or damper closing position and anormally energized thermostatically responsive'electric control circuitsystem yieldably urging the switch in the opposite direction toward theroom cooling or damper opening position.

Yieldnble means The -yieldable means comprises a spring 31 urging switcharm 28 toward damper closing contact 26. When unopposed, this spring isstrong enough to pull arm 28 past the neutral position arm 27 over intoengagement with contact 26.

Control circuit system The control circuit system conventionallyincludes: a relay coil 35 for operating the` motor control switch; anamplifier 36 for operating the relay coil; and a potentiometerorWheatstone bridge 45 for operating the amplifier.

The relay coil 35, when energized, magnetically urges switch arm 28toward the damper opening position. Under low room temperatureconditions, coil 35 is energized by a weak current so that the magneticforce it exerts is overcome by the spring 31. Consequently, arm 2.8willengage, and remain in contact with, damper closing contact 26. With anintermediate degree of energization, which corresponds to normal roomtemperature, the coil 35 will overcome spring 31 sufficiently to pullarm 28 over to the neutral position where it engages neutral arm 27.With strong energization corresponding to high roomtemperatureconditions, the coil 35 will overcome both spring 31 and theresiliently held arm 27 to pull arm 28 over into engagement with contact25 inthe, damper opening circuit. It may be noted that the switch meansin the motor operating circuit and coil 35 in the control circuit areconventionally shown in the form of a relay.

The amplifier 36 is of a conventional type which, when energized througha power connection, operates to magnify or amplify the energy itreceives from the Wheatstone bridge and energize coil 35 accordingly.Since it is of a conventional type, it. should suice to say that l' ithas power terminals 37 and 38 for connection to power and controlterminals 39 and 40 for connectionto the Wheatstone bridge. Terminal 39is a ground connection while terminal 40 is connected to the Wheatstonebridge through line 41.

The Wheatstone bridge is of a conventional type which, when energized,operates in response to low, predetermined and high room temperatures tofeed relatively low, intermediate and strong currents to the amplifier.Accordingly, the bridge has power receiving terminals 46 and 47 andenergy delivering terminals 48 and 49. The power receiving terminals 46and 47 are connected by lines, not shown, to the secondary windingterminals of a transformer 45a forming a part of the amplifiertransformer which, in turn, is connected to power through terminals 37and 38. The power delivering terminal 48 1s connected through ground tothe grounded terminal 39 of the amplifier while bridge terminal 49 isconnected through line 41 to the amplifier terminal 40. One leg. of thebridge 45 contains room thermostat 50 of the teslstance type whilel thediagonally opposite portion of the other leg of the bridge contains ablower outlet thermostat 51 also ot the resistance type, this latterthermostat being, located in the outlet air stream of blower 4 as showninFigure 1.

POWER CONNECTION The motor 4a which drives blower 4, the amplifier 36,the Wheatstone bridge are all connected through a main switch unit 55 toincoming power lines 56 and 57. In conventional operation, the dampermotor lead lines 20 and 30 are also connected through 55 to power. Themain switch unit 55 may` be of any conventional hand-controlled singlepole type or automatic type which is operated by one or more independentroom thermostats to apply power when the room temperature vfalls below aminimum value during the nighttime.

CONVENTIONAL OPERATION We assume that the main switch unit 55 is closed,that the room temperature is at a normal predetermined value, and thatthe damper is at its mid-position. With this assumption, the bridge 45will be unbalanced to an intermediate degree feeding an intermediatecurrent to` the amplifier which, in turn, energizes the relay coil 35 toan intermediate degree holding arm 28 of the motor switch means in theneutral position.

With this assumption, if the room temperature rises above the normalpredetermined value, the resistance of room thermostat will also riseincreasing the bridge unbalance and correspondingly increasing thecurrent flow from the bridge to` the amplifier with a resultant increasein the energization of coil 35. If this rise in room temperature issuicient, the motor switch will close the room-cooling damper-openingcircuit to actuater the damper in the opening direction. But thisactuation will be relatively small because the damper actuatingmechanism will operate, through the conventional bridge readjuster 60,to change the resistance in the other leg of the bridge and therebyreduce the unbalance enough to open the room-cooling damper-openingcircuit and bring the system once again to a relatively stablecondition. However, if the room temperature continues to rise, theforegoing operation will be repeated.

On the other hand, with the original assumption, if the room temperaturedecreases, the bridge will be unbalanced in the opposite directiondecreasing the current fed by the bridge into the amplifier with aresultant decrease in the energization of coil 35. Itf this decreasev ispronounced enough, spring 31 will effect the closureof the room-heatingdamper-closing circuit. Again, however, the closing movement of thedamper will be restricted by the rebalancing'of the bridge` throughreadjuster 60. v

The outlet thermostat 51 exercises less authoritythan the roomthermostat 50. It is said to exercise 10% authority when it requires al0 degree change in temperature to change its resistance as much as a ldegree changev in room temperature changes the resistance of theroomthermostat. Furthermore, since room thermostat 50 and outlet thermostat51 are located in diagonally opposite sections of the bridge,.theunbalance produced by an increase in the resistance of room thermostat50..corresponding to a l degree rise in room temperature iscounterbalanced by a fallin the resistance of outlet thermostat 51corresponding to a l0 degree decrease in the outlet temperature.Consequently, if the room temperature rises sayl degree` and causes roomtemperature thermostat 50 to open the damper and if'the ensuingtemperature of the air stream, discharged by blower 4,

falls 10 degrees, the resistance ofthe outlet thermostat 51 willdecrease enough to eiect a compensating closing movement of the damper.

Before passing, it may be noted that the foregoingl control system isnormally designedy to bring about a full closure of the damper when theroom temperature reaches a low value of say 71.0"` to hold the damper inthatv posi-V holds it fully open duringall room Vtemperatures above-7that` value.Y Between these limits, it operates to hold tha damper atsome intermediate position and it resets itself to differentpredetermined temperature values with each operation of the roomthermrstat and readjuster 60. For example, if it holds a temperature of72 when the outside temperature falls and causes the room temperature todrop, it will close the damper slightly and the readjuster will thenreset the Wheatstone bridge to a value corresponding to room temperatureof say 71.8 instead of 72. With a further lowering of the outsidetemperature, this resetting action will be repeated until the bridge isreset to a value corresponding to a room temperature of 71.0. Here thedamper is fully closed.

Heretofore, if the Ventilating unit were shut down by opening orinterrupting power supply lines 56 and 57, the entire system would berendered inoperative leaving the damper in whatever position it chancedto be at the time the interruption occurred. This is extremelyobjectionable because, with the damper open at the time of the shutdown, the outside air is free to pass into the room through the unitventilator. With a drastic drop in outside air temperature, the roomtemperature could drop accordingly.

IMPROVEMENT In accordance with the present invention, the damper motorcircuit is connected to power independently of the main switch unit 55so that a deenergization of the control circuit system does not effectthe supply of power to, and the continued operation of, the damper motorcircuit. Consequently, when the switch unit 55 is operated to shut downthe Ventilating unit and deenergize the control circuit system, thespring 3l immediately becomes effective to move switch arm 28 to thedamper closing position and, since the damper motor circuit is then con-.nected to power, it becomes immediately operative to close the damperand then shut down automatically through travel limit switch 24.

I claim as my invention:

1. A control system for a ventilator having a damper to close and openan air flow opening and a motor for operating said damper comprising aselectively energizable control circuit, including temperature sensingmeans, for providing electrical signals indicative of a sensedtemperature departure from a predetermined desired value thereof, anormally energized damper motor operating circuit, switching meansincluded in said damper motor operating circuit responsive to saidelectrical signals for selectively operating said motor to progressivelydisplace said damper in a direction to return the sensed temperature tosaid predetermined desired value, means included in said switching meansresponsive to deenergization of said control circuit for operating saidmotor to displace said damper to a limiting position closing said airflow opening, and means responsive to said last mentioned means fordeenergizing said damper motor operating circuit when said damperreaches said limiting position.

2. A control system for a ventilator having a motor operated damper toclose and open an air ilow opening, comprising: an electric operatingcircuit system for operating the motor in accordance with the positionof motor control switch means movable from a neutral position to damperclosing and opening positions on opposite sides of neutral; balancemeans normally operative at a predetermined temperaturc condition tohold said switch means in neutral, said balance means including meansyieldably urging said switch means to its damper closing position and anormally energized thermostatically responsive electric control circuitsystem yieldably urging said switch in opposition to said yieldablemeans, said energized circuit system being responsive to temperatureconditions rising above said predetermined temperature condition to movesaid switch means toward its damper opening position; and a powerconnection for both systems including a main switch unit for energizingand deenergizing said control circuit system; said yieldable means andoperating circuit system being operable, upon the deenergization of saidcontrol system, respectively to move said switch means to its damperclosing position and to operate the damper in the closing directio vReferences Cited in the tile of this patent UNITED STATES PATENTS

